1. Field of the Invention
The invention relates to the field of in vivo clinical high resolution microfluoroscopy and methodology, and in particular to fluoroscopic imaging systems and methods.
2. Description of the Prior Art
The emphasis in nonevasive radiology is shifted from diagnosis to therapy and is part of a general trend in medicine to less evasive techniques. Rapid progress in imaging technology has eliminated the need for many angiographic procedures, while the development of new materials, miniaturized catheters and instruments have resulted in substitution of nonevasive radiological procedures for the treatment of problems, which were once treated by conventional surgical methods.
This transition in medical practice has also placed new demands on radiographic imaging, especially real-time fluoroscopy. What was one simply an observational method for diagnostic radiology has now become a precision guidance or observational instrument for therapeutic procedures.
However, current microscopic image intensifying-television systems exhibit inadequate submillimeter spatial resolution for the increased demands placed upon real-time fluoroscopic observation. This lack of resolution has become an obstacle to practicing radiologists when attempting to image fine anatomic structures on a real-time basis, even when a high resolution, 1,023 line video system, is used in combination with image intensifier operating in its highest magnification mode. This obstacle, coupled with the increasing use of small guidewires and catheters in peripheral arterial systems, has created a clinical need to effectively image in the submillimeter range during real-time fluoroscopic observation. Present fluoroscopy systems lack the ability to provide the needed magnification with simultaneous contrast resolution at acceptable X-ray exposure rates.
The field of digital fluoroscopy and fluorography has experienced rapid development due to the availability of suitable electronic hardware such as fast analog-to-digital converters that handle high digitization rates required for real-time imaging at video frame rates. Recent improvements in video-based imaging technology, such as those provided by digital frame integration to reduce noise has opened new possibilities for clinical application of microfluoroscopy. While the use of optical magnification through a zoom has been considered for application of medical imaging since at least 1972, see Robbins CD, et al., "High Performance Continuous Zoom X-Ray Image Intensifier, "SPI Proc. 1972; 35: 23-32, and even more recently as shown by Rossi et al., "A Variable Aperture Fluoroscopic Unit for Reduced Patient Exposure, "Radiology 129:799-802 (1978), and Rudin et al., Improving Fluoroscopic Image Quality with Continuously vadable zoom magnification," Med. Fys. 18(5): 972-977 (1991), resolutions have been unsatisfactory and the diminished field of view has resulted and loss of orientation. In other words, the realization of clinical application of optical zoom concepts in radiology have failed to be realized because orientation of the magnified image with respect to the larger structures within the regions of interest is easily lost when proceeding to the magnified stages. For example, small voluntary or involuntary movements by the patients, while under examination, results in movement of the object of interest completely from the field of view at the high magnification levels. Reorientation of the object of interest within the field of view cannot then be performed at the magnified level. The fluoroscopic image must be unzoomed until the macroscopic view is reobtained, the patient reoriented in the field of view, and then rezoomed to the higher magnification. Further, when enlarged or zoomed images are displayed, higher X-ray patient exposure rates are required in order to obtain acceptable signal-to-noise ratios.
Therefore, what is needed is an improvement which can be made to radiographic imaging systems, which is capable of magnifying images and providing visibility of object detail at 150 microns or less at the monitor with table top exposure levels of not more than 5 Roentgens per minute.